Infectious complications, especially those due to bacterial organisms, remain an important cause of morbidity and mortality in children with leukemia or lymphoma, even during remission. Among the abnormal host defense mechanisms which lead to increased susceptibility towards infection in these patients polymorphonuclear neutrophil dysfunctions may play a particularly important role. PMN's from children with leukemia and lymphoma may, in particular, present a defect in bactericidal power, related to a failing intracellular oxidative metabolism. The purpose of this project is to evaluate the bactericidal power of PMN's from leukemic and lymphomatous children, and to establish its relationship with PMN oxidative metabolism. It is further planned to attempt the in vitro correction of the oxidative defect with Clofazimine and with a glucose-oxidase-IgG conjugate, to restore a normal bactericidal power in failing PMN's. Measurement of PMN bactericidal power, oxygen consumption, nitroblue tetrazolium reduction, pentose phosphate pathway activity, and hydrogen peroxide production will be undertaken. PMN function will be studied at all stages of the disease, to differentiate between functional defects caused by the disease itself and drug induced effects. The effect of vinca alkaloid derived drugs will also be studied in vitro, on normal and leukemic PMN's. The long term goal of this study is to determine at which stages of the disease there exists a particularly critical PMN dysfunctional state, and to open the way towards clinical use of substances which might correct these dysfunctions.